1. Field of the Invention
The present invention relates to the fields of medicine and medical devices. More specifically, the present invention relates to pacemakers suitable for use in patients in need, including fetuses, and methods of using them to maintain an adequate heart rate in the patients.
2. Description of Related Art
Various devices for artificially providing an electrical impulse to cause or assist in the regular beating of a heart are known in the art. Such devices, commonly referred to as “cardiac pacemakers”, “artificial pacemakers”, or simply “pacemakers”, have evolved from the relatively rudimentary electrical devices of the late 1950s and the 1960s to the highly sophisticated, programmable devices that are now available. Although there is variation in design and implementation of pacemakers, in general, all of them have a common function: to provide an electrical stimulus to cardiac muscle tissue to cause controlled, rhythmic contraction of the muscle tissue such that blood can be pumped through the heart, thus causing circulation of the blood throughout the body.
The design and use of cardiac pacemakers in adults are well established. In general, adult cardiac pacemakers consist of at least one conductive connector or electrode that attaches to heart tissue on one end and to an electrical lead on the other end. The lead is a relatively long conducting material that connects the electrode to a power supply, typically a lithium battery. Modern cardiac pacemakers include electronics to control the rate of pacing and to keep track of battery power, among other things. Typically, an adult cardiac pacemaker has a size on the order of 10 cc and has one or more leads of about 40-60 cm in length. There are several methods of implanting a pacemaker. These methods include those for epicardial pacing, which involves placing the electrodes in contact with the outer wall of the ventricle (epicardium) to maintain satisfactory pacing. Epicardial pacing is the pacing method of choice for babies because their veins are considered too small for a transvenous system. In contrast, transvenous cardiac pacing, also called endocardial pacing, involves inserting a wire containing an electrode lead into a vein, preferably the subclavian vein, and passing it through the vein to either the right atrium or right ventricle. The procedure is facilitated by fluoroscopy, which enables the physician or cardiologist to view the passage of the electrode lead. Permanent pacing with an implantable pacemaker involves connecting the opposite end of the electrode lead and wire to the pacemaker generator (battery and control unit). The pacing generator, or control/battery unit, is then surgically implanted into the patient's chest (for transvenous systems) or the abdomen (for epicardial systems). In transvenous systems, the entire implanted pacemaker thus includes a relatively long lead that runs from the heart, through a vein, and to a battery pack/control unit implanted in the patient's chest.
While design and use of adult pacemakers is a mature field, the same cannot be said for the design and use of fetal pacemakers. Rather, the field of fetal pacemakers has yet to show a successful design and implementation. To date, fetal pacemakers have been designed based on the same concepts used for adult pacemakers. That is, designs for fetal pacemakers have employed an electrode and long lead connected to a battery unit. The electrode is contacted with the fetal heart tissue, and the battery unit is placed outside of the uterus. Such a design has uniformly met with rapid failure due to movement of the fetus in the uterus, which causes dislodgement of the electrode from the fetal heart tissue.